Phase III of the Diabetes Control and Complications Trial will assess the relationship of metabolic control and the development of microvascular complications over a 7-10 year period in individuals with insulin dependent diabetes mellitus. The 2 year feasibility study, phase II, has shown that: 1) a significant delta in the level of blood glucose control can be demonstrated between standard and experimental groups as assessed by hemoglobin A1C and blood glucose values; 2) the relative efficacy, utility, patient acceptability, and safety of the two forms of therapy has been demonstrated; and 3) the biochemical and pathogenic characteristics can be measured and documented with acceptable precision and accuracy. The favorable outcomes for the feasibility phase have provided the basis to start phase III of the trial. The following protocol, as used in phase II, will be continued and implemented in phase III. The experimental treatment will consist of 3-4 daily injections of insulin or an insulin pump, blood testing, and a specified meal plan. This group is telephoned weekly and seen in the clinic for monthly visits. The standard treatment group therapy consists of 1-2 injections of insulin daily, urine testing, blood testing, and a specified meal plan. This group is seen every 3 months in the clinic. During their quarterly visits, both groups have identical laboratory analysis sent to the laboratory and other objective measures to assess the complications of diabetes. Standardization forms are completed on all volunteers and they are sent to the Biostatistics Coordinating Center for tabulation and analysis of data. The International Diabetes Center currently has 11 volunteers in the phase II DCCT group. Six of the volunteers are in an experimental group and 5 in the standard group. Initial recruiting for phase II started in March, 1985 and at the present time, 5 additional patients have been added to the standard group and 2 to the experimental group. Recruitment, as of January 1, 1986, is planned to continue at the rate of 1.4 patients per month until the goal of 55 patients is reached.